These bivalves were at their peak in the Jurassic and Cretaceous periods, when they sat in huge muddy oyster beds in shallow tropical seas. The genus survived a long time, but went extinct about 34 million years ago (mya).

The oyster shell has two 'valves': a larger gnarly-shaped shell (the 'toenail') and a smaller, flattened shell, the 'lid'.[1] The soft parts of the animal lived in the gap between the two shells, just like modern oysters. The shells have prominent growth bands. The large curved shell sat in the mud on the sea floor.